PROJECT SUMMARY Each year 750,000 American experience a heart attack, many of whom progress to heart failure. Heart failure, which accounts for 10% of annual deaths in the United States, is characterized by insufficient pumping that restricts the blood supply to peripheral organs. Current treatments cannot mitigate this decline as they do not address the fundamental problem of cell loss. Stem cell derived cardiomyocytes represent an unlimited, personalized therapy with demonstrated potential to regenerate this contractile function. Recently, the transplantation of stem cell derived cardiomyocytes restored heart function in rhesus monkeys with surgically induced heart attacks. The dramatic improvement in this highly translational model is attributed at least in part to the contractile force generated by the transplanted cells. Despite this improvement in function, only ~5% of cells survived after 4 weeks. Tissue engineering represents one approach to improve the re-muscularization strategy by replicating the cellular and extracellular matrix composition of the heart. In the heart, cells are oriented in a double helical, three-dimensional architecture. This orientation generates twist akin to wringing a wet rag. This twist helps scale a cardiomyocyte?s 15% shortening and 8% thickening to a 65% ejection fraction. Towards generating a personalized therapy capable of adapting to the size and position of an individual?s heart attack, we aim to recapitulate the architecture and torsional function of myocardium. The central hypothesis of this proposal are: 1) replicating the physiological twist of myocardium is necessary for cardiac re-muscularization, and 2) 3D bioprinting aligned cardiac sheets with physiologically relative changes in orientation will generate twist. Importantly, this approach is complementary to previously developed, 3D printed vascularization strategies and enables a scalable and tailorable approach. Overall, this project aims to generate a more physiological tissue that can be used to study physiological indicators of contractile function, which will inform in vivo studies that aim to re-muscularize the heart. In addition, such tissue may help elucidate disease mechanisms previously unidentifiable with simpler in vitro models. Aim 1: Generate a printable bioink composed of aligned, anisotropic cardiac ?tissues. Aim 2: 3D bioprint ?tissue-laden inks into uniaxially aligned cardiac tissue sheets. Aim 3: Determine how relative alignment between 3D bioprinted layers impacts parameters of twist.